Comprehensive Characterization of the Electronic Structure of U⁴⁺ in Uranium(IV) Phosphate Chloride

Emerald-green single crystals of U­(PO₄)Cl were grown by chemical vapor transport in a temperature gradient (1000 → 900 °C). The crystal structure of U­(PO₄)Cl (<i>Cmcm</i>, <i>Z</i> = 4, <i>a</i> = 5.2289(7) Å, <i>b</i> = 11.709(2) Å, <i>c</i> = 6.9991(8) Å) consists of a three-dimensional network of [PO₄] tetrahedra and bicapped octahedral [U^IVO₆Cl₂] groups. Polarized absorption spectra measured for two perpendicular polarization directions show a large number of well-resolved electronic transitions. These transitions can be fully assigned on the basis of a detailed ligand-field treatment within the framework of the <i>angular overlap model</i>. The magnetic behavior predicted on the basis of the spectroscopic data is in agreement with an f ² system and perfectly matched by the results of temperature-dependent susceptibility measurements